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J L Puel

Publications and source records attributed to J L Puel.

48 records · Page 3Linked to original sources
PubMed1988

The active process is affected first by intense sound exposure.

Evidence exists to suggest that intense sound releases excess neurotransmitter from the inner hair cells. However, it has been previously reported that intense sound affects the cochlear micromechanics by altering the stereocilia. Therefore, we tested the hypothesis that intense sound affects structures involved in transduction before it affects the nerve endings. In order to test this hypothesis, we examined the interaction of intense sound with kynurenate which blocks the action of the neurotransmitter on the afferent nerve endings. Intracochlear perfusion of artificial perilymph containing 5 mM kynurenate did not reduce the effect of intense sound when we compare the results with a control group perfused with artificial perilymph alone. These results show that blockade of afferent transmitter receptors did not reduce the effect of acoustic trauma, and the acoustic trauma used herein affected structures involved in transduction before it affected the postsynaptic structures. We speculate that the active process is affected first during acoustic trauma. This interpretation is consistent with the notion that stereocilia are structures that make up part of the active process.

Action Potentials↗
PubMed1988

An ipsilateral cochlear efferent loop protects the cochlea during intense sound exposure.

One suggested physiological function of the efferent nerve fibers innervating the cochlea is that they protect the cochlea against the effects of intense sound exposure. In order to test this hypothesis, we studied the effects of intense sound in the presence and in the absence of strychnine which blocks the efferent nerve fibers. The results show that in presence of strychnine an ipsilateral intense sound has a greater effect on the cochlea than in the absence of strychnine. We conclude that the ipsilateral cochlear efferents may act as protectors against intense sound exposure.

Action Potentials↗
PubMed1988

2-Amino-4-phosphonobutyric acid receptors are not involved in synaptic transmission from hair cells to auditory neurons.

The chemical 2-amino-4-phosphonobutyric acid (APB, AP4), an excitatory amino acid antagonist, was perfused through the guinea-pig cochlea while monitoring various cochlear potentials. The drug (0.6-10 mM) had no effect on the magnitude of the compound action potential of the cochlear nerve, N1 latency, cochlear microphonics, or the summating potential (SP). The results are consistent with the hypothesis that the APB receptor is not involved in neurotransmission between cochlear hair cells and afferent nerve fibers.

Action Potentials↗
PubMed1987

Correlative development of cochlear action potential sensitivity, latency, and frequency selectivity.

The present study was undertaken in order to study the rate of maturation of the cochlear action potential sensitivity, latency, and tuning curves for various stimulus frequencies and to correlate the development of latency and frequency selectivity with threshold development. This study showed a two-stage model of maturation in which thresholds and latencies declined rapidly and linearly during the first stage, and slowly and exponentially during the last stage. These results suggest that latencies and thresholds are influenced by similar maturational processes. The correlative study of frequency selectivity and thresholds showed a linear relationship during the period of rapid maturation, and conversely, a dissociation between the development of tuning and threshold during the late period of slow acquisition of adult sensitivity. This dissociation was particularly marked at 8 kHz where Q10 values continued to increase even when thresholds were adultlike. These results were discussed in relation to anatomical and functional data available from the rat cochlea.

Age Factors↗
PubMed1987

Stereocilia and tectorial membrane development in the rat cochlea. A SEM study.

Maturation of the rat cochlea, from postnatal days 2 to 60, was studied using scanning electron microscopy (SEM), with emphasis on stereocilia and tectorial membrane (TM). Two days after birth, the organ of Corti was very immature. An adult appearance of its surface was observed by day 16 in the basal turn, and by the end of the 3rd postnatal week in the apex. Stereocilia started their development first on inner hair cells. By contrast, the apical pole of outer hair cells ended its maturation before that of inner hair cells. Top-links were detected very early in inner hair cell stereociliary development (postnatal day 2). Marginal pillars temporarily attached the TM to the organ of Corti; they disappeared first in the apical region. This transient attachment seems to play a role in the coupling of outer hair cells to the TM, as prints of their longest stereocilia appeared at the undersurface of the TM by the same time. Moreover, these prints were more clear and regular at the base than at the apex of the cochlea. Results are discussed in relation to ultrastructural and functional data on rat cochlea maturation.

Animals↗
PubMed1987

Modulation of the masking phenomenon by the crossed part of the medial olivocochlear bundle.

The masking phenomenon is used in clinical investigation of the inner ear to determine the frequency selectivity properties of the auditory system. Sectioning of the crossed part of the medial efferent bundle in a guinea pig model decreases the simultaneous masking phenomenon. The efferent effect seen in the forward masking varied with the masking paradigm used. When the masker onset precedes the maskee onset by more than 40 ms, masking diminishes after sectioning the crossed part of the medial efferent bundle. When this duration was shortest (30 ms), no effect was observed. This phenomenon could be explained by the time necessary to stimulate the medial efferent loop. Our results could explain some differences observed in the compound action potential masking curves with different masking paradigms.

Acoustic Stimulation↗
PubMed1987

Functional properties of the crossed part of the medial olivo-cochlear bundle.

The efferent innervation of guinea pig cochleas was sectioned medially, at the level of the floor of the fourth ventricle, to study the effects of the crossed part of the medial efferent pathway on the compound action potential (CAP) masking phenomenon. Sectioning reduced CAP masking for a masker level varying with the frequency of the masker and the time elapsed between the masker onset and the probe onset. Functional properties of the crossed part of the medial efferent tracts: latency, thresholds and frequency selectivity, could be deduced from these data.

Action Potentials↗
PubMed1987

Dose-dependent changes in the rat cochlea following aminoglycoside intoxication. I. Physiological study.

The dose-dependent effects of amikacin on the rat cochlea were studied electrophysiologically using CAP audiograms, amplitude and latency-intensity curves, and CAP tuning curves using a forward masking procedure. The animals were given a daily subcutaneous injection of amikacin in doses ranging from 100 to 1000 mg/kg, for five consecutive days, and were tested one month after the end of the treatment. No functional evidence of ototoxicity was found in animals treated with 100 and 200 mg/kg per day doses of amikacin. The first electrophysiological changes were observed with doses of 300-600 mg/kg per day. They consisted of a broadening of the tip and a hypersensitivity of the tail of the CAP tuning curves, without a change in the CAP threshold sensitivity and latency. Animals treated with 700 mg of amikacin showed an elevation of the tip of the CAP tuning curves and an increase in CAP latency. The classical feature of antibiotic ototoxicity was observed in animals given 800 mg/kg per day of amikacin with an increase in CAP threshold sensitivity and latency, a disruption of the CAP amplitude-intensity function, and a clear hyposensitivity of the CAP tuning curves. These results are discussed in the light of anatomical findings described in a companion paper.

Acoustic Stimulation↗
PubMed1987

Dose-dependent changes in the rat cochlea following aminoglycoside intoxication. II. Histological study.

The structural damages induced by a range of amikacin doses have been studied with SEM and TEM in the adult rat cochlea. Six groups of rats were given daily subcutaneous amikacin injections of either 200, 400, 600, 700, 800, or 1000 mg/kg per day for five consecutive days. Observations were made one month after the end of treatment, following functional recordings [(1987) Hear. Res. 26, 191-197]. In the group treated with 200 mg/kg per day, neither SEM nor TEM revealed any cochlear abnormalities. In the 400-mg group, the only damages were cytoplasmic abnormalities in the OHCs. Changes in the OHC stereocilia occurred at higher doses and were always associated with severe alterations of the underlying cell body. The first missing hair cells were OHCs in the apical regions of the cochleas of the 600-mg group. In the 700-mg group, the loss of OHCs extended to the middle and basal regions, mainly in the third row. By contrast, in the 800- and 1000-mg groups, the usual pattern of hair-cell degeneration was found. Loss of hair cells was greatest in the basal cochlear regions, where the first row of OHCs was more extensively destroyed. These results indicate that metabolic disorders (only visible with TEM) precede stereociliary alterations. Under SEM, the pattern of hair cell degeneration appeared to depend on the dose of the drug. The study clearly demonstrates that both SEM and TEM are needed to determine the true condition of hair cells after drug intoxication.

Amikacin↗
PubMed1987

Development of 2f1-f2 otoacoustic emissions in the rat.

2f1-f2 otoacoustic emissions have been recorded from the rat cochlea during its development. Acoustic responses were recorded at 3, 5 and 7 kHz using a fixed value of the f2/f1 ratio (= 1.17). The first 2f1-f2 acoustic responses were obtained at 12 days after birth for 2f1-f2 = 7 and 5 kHz, and 2 days later for 2f1-f2 = 3 kHz. Adult-like patterns of the acoustic responses were achieved by day 18 for 2f1-f2 = 3 kHz, by day 20 for 2f1-f2 = 5 kHz and by day 28 for 2f1-f2 = 7 kHz. These results are discussed in relation to the available anatomical and functional data on the cochlear development of the rat. The delayed appearance of the 3 kHz acoustic responses might be related to the basal-to-apical gradient of morphological cochlear maturation. The fact that the 2f1-f2 otoacoustic emissions reached adult characteristics from the low to high frequencies is consistent with the development of the tuning properties of the basilar membrane. The long development of the 2f1-f2 acoustic responses at 7 kHz suggests that the organ of Corti undergoes subtle changes well after the end of its apparent maturation.

Aging↗
PubMed1987

[Latency, threshold and frequency selectivity of the crossed medial cochlear efferent pathways].

The efferent innervation of guinea pig cochleas was sectioned medially, at the level of the floor of the fourth ventricle, to study the effects of the crossed part of the medial efferent pathway on the compound action potential (CAP) masking phenomenon. Sectioning reduced CAP masking for a masker level varying with the frequency of the masker and the time elapsed between the masker onset and the probe onset. Functional properties of the crossed part of the medial efferent tracts: latency, thresholds and frequency selectivity, could be deduced from these data. This intensification of the masking phenomenon permitting the improvement of the signal to noise ratio, may thus be attributed to the crossed part of the medial efferent bundle which innervates the outer hair cells.

Animals↗